1. Field of the Invention
This invention relates to an ignition charge for the initiator of a gas generator, particularly an electric gas generator, suitable for the purpose of actuating a seatbelt pretensioner or an airbag inflator, a method for the production thereof, and a method for the production of an initiator using the ignition charge.
2. Description of the Prior Art
Generally, wheeled vehicles, such as automobiles, are provided with a safety device, such as a seatbelt or an airbag, with a view to protecting a driver and a fellow passenger from the impact inflicted in case of collision. The seatbelt, for example, has a quick winding means attached to a device for winding a belt and, in an emergency arising from an accident, is enabled to protect infallibly the driver and the fellow passenger from the impact of collision by actuating the quick winding means and consequently causing the seatbelt to be instantaneously wound up.
As the quick winding means of this kind, numerous devices that utilize a gas generator adapted to generate a gas by the combustion of an explosive have been in great vogue. They operate on the principle that a belt is quickly wound by causing an explosive in the gas generator to burn by means of an electric ignition device including a pair of current conducting pins adapted to be actuated by an impact taking place in case of collision and harnessing the pressure of the resultant gas of combustion for instantaneously driving the piston and the body of rotation of a cylinder.
While this electric initiator uses an ignition charge, it used to make use of an ignition charge that contained lead formed mainly of tricinate (lead styphnate) sensitive to temperature. Since a regulation for controlling the use of an ignition charge containing lead, a substance for environmental load, has recently been rigidified, the ignition charge using a mixture of a flammable substance containing no lead and comprising zirconium and an oxidizing agent containing no lead and comprising potassium perchlorate has been finding acceptance.
For this ignition charge, the method which comprises adding a binder and a solvent to a powdery flammable substance consisting of zirconium, etc. and a powdery oxidizing agent consisting of potassium perchlorate, pelletizing the resultant mixture by the use of a stone mill, subsequently unifying the resultant pellets into a granular ignition charge, measuring a prescribed volume of the ignition charge and squeezing the measured ignition charge on an exothermic element is available.
Besides, the method which, as disclosed in JP-A 2004-115001 and JP-A HEI 9-210596, for example, forms an ignition charge by dispersing a flammable substance and an oxidizing agent in a solvent, converting the resultant dispersion into a slurry, dropping this slurry onto an exothermic element and drying the wet ignition charge is available.
The ignition charge obtained on the exothermic element by these methods is manufactured, by disposing a case, a pin and a resin mold around it, into an initiator.
In the initiator configured as described above, when the impact arising in case of collision is inflicted as an electric signal to a pair of current conducting pins, the exothermic element disposed between the current conducting pins begins to generate heat and the heat sets the ignition charge aflame and then actuates the gas generator for a seatbelt pretensioner or the inflator for an airbag.
When the gas generator for the seatbelt pretensioner is actuated, the pressure of the resultant gas of combustion instantly actuates the quick winding means of the seatbelt. When the inflator for the airbag is actuated, the pressure of the resultant gas of combustion instantaneously inflates the airbag.
The conventional ignition charge for use in the initiator, as described above, has been obtained in the form of granules by a procedure that comprises adding a binder and a solvent to a powdery flammable substance consisting of zirconium and a powdery oxidizing agent consisting of potassium perchlorate, pelletizing the resultant mixture by the use of a stone mill, and subsequently imparting a uniform size to the pellets. Further, the prescribed volume of this ignition charge is measured and then squeezed onto an exothermic element. Since this method is required to limit the solvent to a small amount during the course of pelletization, however, it has a high possibility that the ignition charge will catch fire during the course of its production owing to the friction occurring as in the stone mill. Though the reliability of ignition is high because the exothermic element and the ignition charge are made to adhere by the squeezing, the possibility of deriving ignition from the same friction as in the case of the pelletization is high because the squeezing is implemented by the use of a granular drying agent. Thus, the security of safety in terms of production has constituted a serious problem.
The method that forms an ignition charge by dispersing a flammable substance and an oxidizing agent in a solvent, thereby forming slurry, subsequently dropping the slurry on an exothermic element and drying the wet exothermic element as described above has been proposed in JP-A 2004-115001 and JP-A HEI 9-210596. This method is capable of greatly easing the influence of the friction during the intimate mixing because the amount of the solvent is large and the mixture assumes the form of slurry. When the amount of the solvent in this slurry is unduly large, however, the part contacting the exothermic element part suffers occurrence of air gaps and holes while the solvent in the ignition charge formerly dropped onto the exothermic element part is dried, with the result that the reliability of ignition will be seriously degraded. In contrast, when the amount of the solvent in the slurry is unduly small, the shortage results in not only rendering security of uniform intimate mixing infeasible but also degrading markedly the reliability of contact with the exothermic element part. Thus, the problems have inevitably occurred in the ranges of compositions disclosed in JP-A 2004-115001 and JP-A HEI 9-210596.
This invention, therefore, has as its object to provide an ignition charge for an initiator aimed at reconciling the safety during the production of the ignition charge and the reliability of ignition, a method for the production thereof, and a method for the production of an initiator using the ignition charge.